How do I get item drops?

I answered a similar question to this: How Do I Get More Guns?. Noticed that your question was posted a few hours before that though.

This is the new "Arms Deal" update which went live on 14/08/2013. Valve released a really good FAQ on it, which can be found here.

The bits of interest for your particular question, "How do I get item drops?":

• Timed weapon drops, just by playing on official and community servers (VAC enabled) in any game mode.
• Opening dropped weapon cases with a weapon case key.
• Trade weapons with other players through Steam's Trading interface.
• Purchase them from other players through the Steam Marketplace.

Regarding the first point, these are obtained for play time over the course of a week. As your play time increases, the drop rate will slow down. This is reset when the week rolls over. Not sure the start day or time of a week though.

I'm not 100% sure where you will get the weapon case keys. The below quote suggests that you buy these:

This update will also actively support the CS:GO competitive community with the introduction of the eSports Weapon Case. A portion of the proceeds from sales of eSports Case Keys will go towards prize purses at competitive events.

Hope that helps.

You will get 2 drop maximum each day an a total of 4 each week. Half will be weapons, and half will be crates. That means that you will get 1 gun and 1 normal crate one day, and the other day you will get one weapon and one e-sports crate. If you don't want to play but still want drops, you can go to servers that are dedicated to idling.

Also, if you are interested in good quality, your best bet is to open crates. My experience is that the skins you get dropped don't have very good quality (field tested, well-worn etc.)